1. Field of the Invention
The invention relates to a controller for an internal combustion engine and more particularly, to a controller for an internal combustion engine that includes a rotational phase difference changing mechanism that changes the rotational phase difference of a camshaft with respect to a crankshaft and a valve operating characteristic changing mechanism that changes the operating characteristics of a valve with respect to the rotation of the camshaft.
2. Description of the Related Art
Published Japanese Translation of PCT Application No. 2006-520869 (JP-A-2006-520869) describes a valve mechanism that is able to change the operating characteristics of a valve. The valve mechanism includes a cam carrier that is immovable in the rotational direction and movable in the axial direction with respect to a camshaft. The cam carrier has a cam having two different cam tracks. The cam carrier is moved in the axial direction by an actuator device to switch between the cam tracks of the cam that actuates the valve. By so doing, the operating characteristics of the valve are changed.
In the valve mechanism described in JP-A-2006-520869, a mechanism that includes a spiral groove formed in the cam carrier and an electric actuator that engages or disengages a drive pin with or from the groove is used as the actuator device that moves the cam carrier in the axial direction. When the drive pin is engaged with the groove by the electric actuator during rotation of the camshaft, the cam carrier moves in the axial direction through contact between the drive pin and the groove.
JP-A-2006-520869 does not specifically describe the timing at which the drive pin is engaged with the spiral groove. However, it is important how to control the above timing in control on the valve mechanism. If the timing at which the drive pin is actuated is wrong, it is difficult to properly engage the drive pin with the spiral groove. As a result, there is a possibility that the operating characteristics of a valve cannot be changed or the operating characteristics of a valve are changed with a delay. When the valve mechanism is a valve stop mechanism described in Japanese Patent Application Publication No. 2003-074385 (JP-A-2003-074385), it is difficult to stop a valve at a desired timing. Furthermore, if the drive pin fails to be properly engaged with the spiral groove, there is a concern that the groove and/or the drive pin wear or there is a concern that the drive pin is damaged.
Generally, the timings of various controls in an internal combustion engine are mostly controlled by a signal from a crank position sensor. This may also be applied to the valve mechanism described in JP-A-2006-520869. That is, the timing at which the drive pin is actuated may be determined on the basis of a crank position calculated from a signal of a crank position sensor.
Incidentally, when an internal combustion engine includes a variable valve timing mechanism described in Japanese. Patent Application Publication No. 2003-254017 (JP-A-2003-254017), there is a concern that the timing at which the drive pin is actuated is wrong. This is because, as the variable valve timing mechanism operates, the rotational phase difference of the camshaft with respect to the crankshaft is changed and then the positional relationship of the spiral groove with respect to the crankshaft also changes. When the timing is controlled on the basis of a signal from the crank position sensor, the variable valve timing mechanism operates to make it difficult to engage the drive pin with the groove at an appropriate timing.